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Vulnerability of coral reefs

Vulnerability of coral reefs. Presented by Janice Lough. Authors.

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Vulnerability of coral reefs

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  1. Vulnerability of coral reefs Presented by Janice Lough

  2. Authors This presentation is based on Chapter 5 ‘Vulnerability of coral reefs in the tropical Pacific to climate change’ in the book Vulnerability of Tropical Pacific Fisheries and Aquaculture to Climate Change, edited by JD Bell, JE Johnson and AJ Hobday and published by SPC in 2011. The authors of Chapter 5 are: Ove Hoegh-Guldberg, Serge Andréfouët, Katharina Fabricius, Guillermo Diaz-Pulido, Janice Lough, Paul Marshall and Morgan Pratchett

  3. Moving reefs out of their comfort zone Source: Hoegh-Guldberg et al. (2007)

  4. Outline Coral Reefs • Key coastal ecosystem • Many different reef types • Narrow environmental limits • Already shown impacts, e.g. bleaching • Combined effects of disturbances • Less time to recover • Simpler reefs • Healthy reefs will cope better

  5. Many different types of reefs • 13/22 PICTS have more reef than land area • Dominant coastal habitat • Majority are oceanic • Great diversity of reef types

  6. With different levels of human use • Support local fisheries • Differences in local pressures

  7. Location matters • Fringing continental reefs affected by river runoff • Isolated oceanic reefs not well connected e.g. larval supplies • Tropical cyclones >10o from equator • El Niño/La Niña impacts

  8. Important environmental factors • Warm water temperatures • Shallow well-lit waters • Low sediment and nutrients • Right ocean chemistry Ω >3.3 • Warmest parts of oceans • Narrow temperature range

  9. Corals must build skeletons fast enough to withstand natural forces of erosion Photos: AIMS

  10. A special relationship • Symbiosis at heart of tropical coral reefs • Photosynthetic algae live within coral animal • Corals get enough energy for rapid calcification • Form structurally complex reefs • Home to thousands of other plants and animals Photo: Michael ten Lohuis Photo: AIMS

  11. Relationship breaks down due to stress • Stressed corals lose algae (and their pigments) • Coral bleaching • Seen more frequently due to warmer temperatures • Corals living only ~1-2oC below upper thermal limit • Too much fresh water also causes bleaching Photos: Ray Berkelmans

  12. Ocean acidification • 30% extra CO2 entered oceans • Otherwise greater warming! • BUT changes ocean chemistry • Harder to form skeletons and shells • More erosion

  13. Ocean acidification: natural laboratory • High CO2 volcanic seeps, PNG • ‘Winners’ = massive corals • ‘Losers’ = branching, tabulate corals • Reduced coral diversity • Much simpler reef with lower pH Source: Fabricius et al. (2011)

  14. Warmer temperatures • Very high vulnerability • Already seen bleaching, diseases

  15. More acidic ocean • High vulnerability • Weakens reef framework

  16. Stronger storms and heavier rainfall • Moderate vulnerability • More disturbances = less time to recover

  17. Higher sea level • Some corals may keep up • Loss of deeper corals

  18. Management interventions Source: Anthony & Maynard (2011)

  19. What it means for coral reefs • Already shown vulnerability • Bleaching and diseases • Physical destruction • Weaker skeletons • Lower salinity • Connectivity between reefs • Direct and indirect effects on other reef organisms

  20. Summary key issues • Rates of change • Combined stressors • Less time to recover between disturbances • Adaptation in decades instead of 1000’s years??? • Healthy reefs better able to cope • Consequences for reef-dependent fisheries Coral reefs will not disappear entirely BUT are likely to be MUCH SIMPLER ECOSYSTEMS

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